Relays and contactors are known devices used for switching of intended circuits/loads and the like. A relay is an electrically operated switch. Many known relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low power signal or where several circuits must be controlled by one signal. A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.
In general, a simple electromagnetic relay consists of a coil assembly, a movable armature and one or more sets of contacts, i.e. single throw system, double throw system, etc. The sets of contact include movable contacts, fixed normally open contacts and fixed normally closed contacts. The armature is mechanically linked to one or more sets of moving contacts and is held in place by a spring.
When an electric current is passed through the coil assembly it generates a magnetic field that attracts the armature. The consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with a fixed contact(s). If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by the spring force of the return spring toward its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays and contactors are manufactured to operate quickly. In a low-voltage application, this reduces noise; in a high voltage or current application, it reduces arcing. In order to allow the proper movement of the contacts, the spring force is designed to be less than the force generated by the coil.
However, in many contactors, electromagnetic repulsion generated by the constriction of the flow of current through the contacts can prevent or inhibit the contacts from closing properly or can cause the contact to improperly open due to a large transient pulse applied during operation. Generally in such applications, a large spring force of a contact spring is provided to overcome or counteract the electromagnetic repulsion. The large spring force provides contact pressure between the movable contactor and the fixed contactor, thereby maintaining the contacts in a closed position.
In order to increase the contact pressure generated by the contact spring, the size of the spring must be increased. Consequently, the force generated by an electromagnet, which drives the movable contactor, must also be increased, requiring a larger electromagnet. This results in the size of the entire structure being increased.
It would therefore be beneficial to provide a contactor assembly in which the contacts are maintained in a closed position without the need to increase the size of the assembly. In particular, it would be beneficial to provide a contact assembly which uses electromagnetic forces to resist or counteract the electromagnetic repulsion of the contacts.